http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
cydAB operon is required for intracellular survival of Brucella abortus S2308
B. abortus S2308 is a Gram-negative, facultative, intercellular bovine pathogen that is transmissible to humans. Brucellosis in the bovine host is characterized by the multiplication of B. abortus in the utrine trophoblastic epithelium of pregnant ruminants, the final outcome of which is abortion. Scant information exists about the molecular mechanisms employed by B. abortus to combat host defenses to persist and replicate in host cells. The lack of an efficient vaccine to treat Brucella infections in animals, and its potential applicability in biological warfare highlights the importance of elucidating mechanisms involving virulence and intercellular survival of this pathogen. To resist an environment of low pH. reactive oxygen intermediates, and nutrient deprivation inside host microphones, B. abortus synthesizes proteins that are required for intercellular survival. Transposon (Tn5 ) mutagenesis of B. abortus and the subsequent screening of mutants for sensitivity to killing in murine microphones and attenuated survival in the BALB/c mice, led to the identification of a mutant severely attenuated in both microphones in vitro, and mice spleens in vivo. This mutant was interrupted in a locus homologous to the 5' end of the cydB, a gene which is part of the cydAB operon that is involved in aerobic respiration in prokaryotes. This operon encodes for cytochrome bd oxidase, a ubiquinol oxidase that is expressed under microaerobic conditions as the organism reaches stationary phase, and catalyzes the terminal step of the electron transport chain, reducing molecular O₂ to H₂O. The B. abortus cydB::Tn5 mutant shows a heightened sensitivity to H[]O[], is attenuated in the presence of respiratory inhibitors NaN₃ and ZnSO₄, has diminished viability at acidic pH in vitro, and does not survive at stationary phase. Complementation of the cydB::Tn5 mutant with a wild-type copy of the cydAB operon restored survival in mice, and tolerance to acid, H₂O₂, and respiratory inhibitors. On introduction of the genes for CuZnSOD and catalyst from B. abortus in the cydB::Tn5 strain, restored its survival in mice, although not to wild-type levels. This suggests that attenuation of these mutants might be resulting from a buildup of ROIs, due to the absence of a functional electron transport chain.
Issued also on microfiche from University Microfilm Inc.
Includes bibliographical references (leaves 82-107).